Electrostatic instrument.



PATENTED OCT. 11, 1904.

F. H. BOWMAN. ELECTROSTATIC INSTRUMENT.

APPLICATION FILED NOV.25,1903.

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UNITED STATES Patented October 11, 1904.

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FRANCIS H. BOWMAN, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEIV YORK.

ELECTROSTATIC INSTRUMENT.

SPECIFICATION forming part of Letters Patent No. 771,968, dated October11, 1904. Application filed November 25, 1903. Serial No. 182,624. (Nomodel.)

To all whom it may concern.-

Be it known that I, FEANoIs H. BOWMAN, a citizen of the United States,residing at Lynn, county of Essex, State of Massachusetts, have inventedcertain new and useful Improvements in Electrostatic Instruments, ofwhich the following is a specification.

This invention relates to an electrostatic ground-detector, aninstrument for indicating the occurrence of a ground and the line whichis grounded, though the invention is applicable to other electrostaticinstruments, such as voltmeters.

The object of the invention is to provide an instrument which canreadily be adapted for use on circuits differing widely in voltage andwhich shall be more compact than those now in use.

Electrostatic instruments have been commonly constructed with a pivotedvane mounted to rotate between pairs of stationary conducting plates orquadrantsf the quadrants of each pair being connected to one of theseveral lines or to ground and mounted with one quadrant above and onebelow the moving vane. In these instruments the force exerted on themovable vane tending to turn it on its pivot depends on the distancebetween the vane and the stationary quadrants and the potential of thequadrants. As an electrostatic ground detector is not required to givean indication to an exact scale, it may be used without change oncircuits differing in voltage over a considerable range; but when aninstrument of this type has been constructed for use on a comparativelyhigh-voltage circuit it cannot be used on a low-voltage circuit, as thedistance between the quadrants of any pair, or, more correctly, betweeneach quadrant and the moving vane, is so great that the torque developedin the moving element is insufiieient to give a positive indication. Ihave therefore provided an electrostatic instrument having auxiliaryquadrants in addition to the pairsof stationary quadrants which may bereadily mounted between the main quadrants and electrically connectedthereto to increase the area of active surface and reduce the air-spacebetween the parts rod of resistance material, in the connectionsbetweenthe several quadrants and the lines and ground, so that only a smallcurrent would pass if a connection from one pair of quadrants to anotherwere closed by a breakage or the formation of an are. I effect a furtherimprovement in the construction of the instrument by mounting theseresistancerods within the studs by which connection is made to thequadrants and arranging the rods to be'readily removable from the studs.By this construction the instrument occupies less space, presents aneater appearance, and the resistances may be quickly removed and newones inserted.

My invention therefore comprises an electrostatic instrument havingauxiliary conducting surfaces or quadrants removably mounted incooperative relation to the-movable vane to increase the sensitivenessof the instrument.

It also comprises an electrostatic instrument having resistancesremovably mounted in the studs by which connection is made to theinstrument.

It further comprises other novel features which will be more fullydescribed hereinafter and definitely indicated in the appended claims.

In the accompanyingdrawings, which illustrate one embodiment of myinvention, Figure 1 is a top view, broken away in part, of anelectrostatic grounddetector. Fig. 2 is a section'on line 2 2 of Fig. 1,one of the studs being shown in section. Fig. 3 is a perspective view ofa pair of the auxiliary quadrants, and Fig. 4: is a diagrammatic view ofthe electrical connections.

The instrument is inclosed in a metallic casing 1, having a glass front2 and mounted on 6, carrying a vane 7 is pivotally mounted at thatcenter on a frame 8, supported from the back of the casing. Shaft 6carries a needle or indicator 9, mounted to sweep over a scale 10,supported from the back of the casing by a post 11, to indicate by itsdeflection the condition of the electrostatic surfaces which control themoving vane 7 An adjustable counterweight may be provided on shaft 6 tonormally center the indicator with relation to the dial, and two lightsprings 12 12 may also be provided, as shown in Figs. 1 and 2, toprevent excessive Vibration of the indicator. A more detaileddescription of these parts is not considered necessary, as they form nopart of my invention.

The electrical connection to the quadrants is made through the studs orposts 4, by which they are supported. As shown in Fig. 2, the twoquadrants of each pair are securely held on the ends of a metallic rod13, having a threaded extension 14, which screws into a metallic block15. This block fits within a bushing 16, of wood, rubber, or otherinsulating material, which extends through an opening in the back of thecasing and is provided with a flange which engages the casing. Theportion 'of bushing 16 within the casing is covered with a cap 17, alsoof wood or rubber, corrugated to increase its surface. The stud 4 isalso corrugated, as shown, and its end fits into the v bushing 16. Thisstud is provided with a central opening in the end of which a metallicrod 18 is secured by a setscrew or in any other suitable manner. The endof rod 18 is threaded and screws into the opening in block 15 to securethe post in position. At its other end stud 4 is provided with a cap 19,interiorly threaded to receive a plug 20, which has a threaded extensioncarrying nuts 21, between which the connectingwire is held. Within theopening in stud 4 is a spring 22, soldered at one end to plug 20 and atthe other end to a metallic button 23. Also within this casing is ahigh-resistance rod 24, preferably carbon. Spring 22 presses themetallic button 23 into firm engagement with one end of the rod 24 andholds the other end of the rod tightly against the metallic rod 18,insuring good electrical connection between the plug 20 and thequadrants 5, supported on the stud. To remove the resistance-rod 24 inorder to replace it with a rod differing in resistance, the plug 20 iswithdrawn from cap 19, carrying with it spring 22 and button 23. Theresistance rod will then drop by gravity through the opening in stud 4,or the stud itself may be withdrawn by unscrewing rod 18 from block 15.

A ground-detector as thus constructed can be used on circuits varying involtage over a considerable range; but to adapt the instrument for useon a circuit of much lower voltage I provide auxiliary quadrants 25,which are mounted between the quadrants 5 and electrically connectedthereto to increase the area of active surface and decrease the distancebetween the conducting-surfaces connected to line and ground and themoving vane. As shown in Fig. 3, this adapter consists of a pair ofquadrants 25, corresponding in shape to the quadrants 5 and rigidlymounted on a curved piece 26, which fits on post 13 and is tapped toreceive a screw 27, by which the adapter is mounted in place on post 13and electrically connected thereto. The distance between theelectrically-charged parts and the moving vane 7 being thus decreasedand the area of these parts increased, the instrument is rendered moresensitive, and the construction permits removing the auxiliary quadrantsquickly in case it is again desired to use the instrument on thehigh-voltage system.

The electrical connections to the instrument are shown diagrammaticallyin Fig. 4. The upper pairs of quadrants are connected to the lines, asshown, and the lower pairs are connected together by the strip 28 and toground, all connections being made through the studs or posts 4.

I have described herein a ground-detector for use on single-phasecircuits; but it is obvious that the improvements are equally applicableto polyphase electrostatic ground-dedectors and to other electrostaticinstruments.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. An electrostatic instrument having conducting-surfaces, a pivotedvane, and auxiliary conducting-surfaces removably mounted in cooperativerelation to the moving vane.

2. An electrostatic instrument comprising two confrontingconducting-surfaces forming the fixed and movable members of theinstrument, and means for varying the area of active surface.

3. An electrostatic instrument having conducting-surfaces, a pivotedvane, and auxiliary conducting-surfaces removably mounted between saidconducting-surfaces and the moving vane.

4. An electrostatic instrument having conducting-surfaces arranged inpairs, a pivoted vane, and auxiliary conducting-surfaces removablymounted in cooperative relation to the moving vane and in electricalconnection with a pair of said conducting-surfaces.

5. An electrostatic instrument having conducting-surfaces arranged inpairs, a pivoted vane, and pairs of auxiliary conducting-surfaces, eachpair removably mounted between the conducting-surfaces of one of saidpairs and electrically connected therewith.

6. An electrostatic instrument having conducting-surfaces arranged inpairs, a metallic post supporting each pair of surfaces and electricallyconnecting them, a pivoted vane, and auxiliary conductings-urfacesremovably mounted on said posts.

7 An electrostatic instrument having conducting-surfaces arranged inpairs, a metallic post supporting each pair of surfaces and electricallyconnecting them, a pivoted vane, and a pair of auxiliaryconducting-surfaces removably mounted on each post between theconducting-surfaces supported thereon.

8. In an electrostatic instrument, a pair of conducting-surfaces, ametallic post to which said surfaces are secured and by which they areelectrically connected, a pair of auxiliary conducting-surfaces, and ametallic supporting member carrying said auxiliary surfaces andremovably mounted on said posts.

9. Inan electrical instrument, a stud through which electricalconnection is made to the instrument, and a resistance in saidconnection plurality of conducting-surfaces, studs of insulatingmaterial supporting said surfaces, each stud having a longitudinalopening therein,and a removable resistance in the opening in each ofsaid studs in electrical connection with the conducting-surfacesupported thereon.

13. In an electrostatic instrument, a conducting-surface, astud ofinsulating material supporting the same, having an opening therein, ametallic piece held in said opening at one end in electrical connectionwith said conductingsurface, a resistance in said opening, and a springarranged to press the resistance against said metallic piece.

14:- In an electrostatic instrument, a conducting-surface, a stud ofinsulating material supporting the same, having an opening therein, ametallic piece held in said opening at one end in electrical connectionwith said conductingsurface, a resistance in said opening, and a springin electrical connection with said resistance and arranged to press itagainst said metallic piece.

15. In an electrostatic instrument, a stud of insulating material, aconducting surface mounted thereon, an auxiliary conductingsurfaceremovably mounted in electrical connection with said surface, andaresistance inclosed within said stud and electrically connected withsaid conducting-surfaces.

In witness whereof I have hereunto set my hand this 23d day of November,1903.

FRANCIS H. BOWVMAN.

Witnesses:

DUGALD McK. McKILLor, JOHN J. WALKER.

